Establishment of a high throughput screen for the discovery of malaria transmission blocking drugs a major goal of the worldwide malaria eradication program is the reduction and eventual elimination of malaria transmission. In order to achieve this goal, the development of drugs to prevent transmission becomes a high priority and requires new approaches and assays. Herein we propose to develop a small molecule high throughput screen (HTS) focused on preventing the development of gametocytes, the form of malaria that mediates transmission. The goal of this work is the discovery of small molecules that could be developed into transmission blocking drugs. Efforts for the development of vaccines or antimalarial drugs have traditionally targeted the asexual stages of P.falciparum, while virtually neglecting transmission stages. Asexual stages are the proliferative stages during the parasite cycle in the human host, and can reach large numbers (up to 20% of all mature red blood cells in the body may be infected). Asexual development is also linked to the morbidity and mortality of falciparum malaria. However, the emergence of resistance against all currently used drugs (all of which target asexual stages) and unsuccessful attempts to develop vaccines based on asexual blood stage antigens highlight the importance of targeting transmission stages. The global campaign to eradicate malaria, initiated by the Bill and Melinda Gates foundation in 2007, has recognized that inhibiting transmission needs to be the top priority if we aim for eradication. There is a major focus on insecticide research, as well as on drugs and vaccines designed to block transmission of malaria from an infected person to additional hosts, by killing the sexual form of the parasite in the bloodstream or preventing maturation of the parasite within the mosquito. Unfortunately, little is known about the biology of transmission stages, and methods for in vitro culture and analysis are limited compared to asexual stage parasites. My laboratory has established a series of crucial technologies for the standardized culture, the detection and the quantification of these stages in vitro. In fact, these technologies enable us to propose the first high throughput assay with a library of 160,000 of chemically diverse compounds for the discovery of compounds that inhibit the development of malaria transmission stages. This project is a collaboration with the Broad Institute, which will be providing expertise in establishment and performance of the assay as well as compound libraries. This is a very important and timely project with great potential to contribute to improved health conditions in malaria endemic countries. Based on the hit rate of a recent whole cell P. falciparum assay (approximately 1%) at our proposed initial compound concentration, we anticipate identification of several hundred to a few thousand compounds that will be further investigated in dose-down screens. In addition, we will perform a microscopic analysis of corresponding parasite phenotypes to identify possible common patterns on growth inhibition or killing. Although beyond the scope of the experiments proposed for this award, lead compounds will be further analyzed in follow up studies such as secondary assays, animal studies, and through mechanism of action studies for target identification. This work will ultimately feed both a pipeline for further development of transmission blocking drugs and our continuous efforts to understand the biology of these elusive yet important parasite stages. A major goal of the worldwide malaria eradication program is the reduction and eventual elimination of malaria transmission. In order to achieve this goal, the development of drugs to prevent transmission becomes a high priority and requires new approaches and assays. Herein we propose to develop a small molecule high throughput screen (HTS) focused on preventing the development of gametocytes, the form of malaria that mediates transmission. The goal of this work is the discovery of small molecules that could be developed into transmission blocking drugs.